Photovoltaic cells, sometimes called solar cells, can convert light, such as sunlight, into electrical energy.
One type of photovoltaic cell is commonly referred to as a dye-sensitized solar cell (DSSC). As shown in FIG. 1, a DSSC 100 can include a charge carrier layer 140 (e.g., including an electrolyte, such as an iodide/iodine solution) and a photoactive layer 145 disposed between electrically conductive layers 120 (e.g., an ITO layer or tin oxide layer) and 150 (e.g., an ITO layer or tin oxide layer). Photoactive layer 145 typically includes a semiconductor material, such as TiO2 particles, and a photosensitizing agent, such as a dye. In general, the photosensitizing agent is capable of absorbing photons within a wavelength range of operation (e.g., within the solar spectrum). DSSC 100 also includes a substrate 160 (e.g., a glass or polymer substrate) and a substrate 110 (e.g., a glass or polymer substrate). Electrically conductive layer 150 is disposed on an inner surface 162 of substrate 160, and electrically conductive layer 120 is disposed on an inner surface 112 of substrate 110. DSSC 100 further includes a catalyst 130 (e.g., formed of platinum), which can catalyze a redox reaction in charge carrier layer 140. Catalyst layer 130 is typically disposed on a surface 122 of electrically conductive layer 120. Electrically conductive layers 120 and 150 are electrically connected across an external electrical load 170.
During operation, in response to illumination by radiation in the solar spectrum, DSSC 100 can undergo cycles of excitation, oxidation, and reduction that produce a flow of electrons across load 170. Incident light can excite photosensitizing agent molecules in photoactive layer 145. The photoexcited photosensitizing agent molecules can then inject electrons into the conduction band of the semiconductor in layer 145, which can leave the photosensitizing agent molecules oxidized. The injected electrons can flow through the semiconductor material, to electrically conductive layer 150, then to external load 170. After flowing through external load 170, the electrons can flow to layer 120, then to layer 130 and subsequently to layer 140, where the electrons can reduce the electrolyte material in charge carrier layer 140 at catalyst layer 130. The reduced electrolyte can then reduce the oxidized photosensitizing agent molecules back to their neutral state. The electrolyte in layer 140 can act as a redox mediator to control the flow of electrons from layer 120 to layer 150. This cycle of excitation, oxidation, and reduction can be repeated to provide continuous electrical energy to external load 170.
Another type of photovoltaic cell is commonly referred to a polymer photovoltaic cell. As shown in FIG. 2, a polymer photovoltaic cell 200 can include a first substrate 210 (e.g., a glass or polymer substrate), a first electrically conductive layer 220 (e.g., an ITO layer or tin oxide layer), a hole blocking layer 230 (e.g., a lithium fluoride or metal oxide layer), a photoactive layer 240, a hole carrier layer 250 (e.g., a polymer layer), a second electrically conductive layer 260 (e.g., an ITO layer or tin oxide layer), and a second substrate 270 (e.g., a glass or polymer substrate).
Light can interact with photoactive layer 240, which generally includes an electron donor material (e.g., a polymer) and an electron acceptor material (e.g., a fullerene). Electrons can be transferred from the electron donor material to the electron acceptor material. The electron acceptor material in layer 240 can transmit the electrons through hole blocking layer 230 to electrically conductive layer 220. The electron donor material in layer 240 can transfer holes through hole carrier layer 250 to electrically conductive layer 260. First and second electrically conductive layers 220 and 260 are electrically connected across an external load 280 so that electrons pass from electrically conductive layer 260 to electrically conductive layer 220.